An employee of the Monrovia City Corporation sprays disinfectant inside a government building in a bid to prevent the spread of the deadly Ebola virus, in the city of Monrovia, Liberia, Friday, Aug. 1, 2014. U.S. health officials warned Americans not to travel to the three West African countries hit by the worst recorded Ebola outbreak in history. The travel advisory issued Thursday applies to nonessential travel to Guinea, Liberia and Sierra Leone, where the deadly disease has killed more than 700 people this year. (AP Photo/Abbas Dulleh)

An employee of the Monrovia City Corporation sprays disinfectant inside a government building in a bid to prevent the spread of the deadly Ebola virus, in the city of Monrovia, Liberia, Friday, Aug. 1, 2014. U.S. health officials warned Americans not to travel to the three West African countries hit by the worst recorded Ebola outbreak in history. The travel advisory issued Thursday applies to nonessential travel to Guinea, Liberia and Sierra Leone, where the deadly disease has killed more than 700 people this year. (AP Photo/Abbas Dulleh)

China’s Margaret Chan, center, Director-General of the World Health Organization, WHO, is greeted by officials as she arrives at the airport for talks on Ebola in the city of Conakry, Guinea, Friday, Aug. 1, 2014. The death toll from the worst recorded Ebola outbreak in history surpassed 700 in West Africa as security forces went house-to-house in Sierra Leoneâ€™s capital Thursday looking for patients and others exposed to the disease. Fears grew as the United States warned against travel to the three infected countries â€” Guinea, Sierra Leone and Liberia â€” and Sierra Leoneâ€™s soccer team was blocked from boarding a plane in Nairobi, Kenya, that was to take them to the Seychelles for a game on Saturday. (AP Photo/ Youssouf Bah)

An employee of the Monrovia City Corporation mixes disinfectant before spraying it on the streets in a bid to prevent the spread of the deadly Ebola virus, in the city of Monrovia, Liberia, Friday, Aug. 1, 2014. U.S. health officials warned Americans not to travel to the three West African countries hit by the worst recorded Ebola outbreak in history. The travel advisory issued Thursday applies to nonessential travel to Guinea, Liberia and Sierra Leone, where the deadly disease has killed more than 700 people this year. (AP Photo/Abbas Dulleh)

Liberian soldiers walk through streets to prevent panic as fears of the deadly Ebola virus spread in the city of Monrovia, Liberia, Friday, Aug 1, 2014. U.S. health officials warned Americans not to travel to the three West African countries hit by the worst recorded Ebola outbreak in history. The travel advisory issued Thursday applies to nonessential travel to Guinea, Liberia and Sierra Leone, where the deadly disease has killed more than 700 people this year. (AP Photo/Abbas Dulleh)

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CONAKRY, Guinea (AP) â€” An Ebola outbreak that has killed more than 700 people in West Africa is moving faster than efforts to control the disease, the head of the World Health Organization warned as presidents from the affected countries met Friday in Guinea’s capital.

Dr. Margaret Chan, the WHO’s director-general, said the meeting in Conakry “must be a turning point” in the battle against Ebola, which is now sickening people in three African capitals for the first time in history.

“If the situation continues to deteriorate, the consequences can be catastrophic in terms of lost lives but also severe socio-economic disruption and a high risk of spread to other countries,” she said, as the WHO formally launched a $100 million response plan that includes deploying hundreds more health care workers.

Medecins Sans Frontieres, also known as Doctors Without Borders, said the WHO pledge “needs to translate to immediate and effective action.” While the group has deployed some 550 health workers, it said it did not have the resources to expand further.

Doctors Without Borders said its teams are overwhelmed with new Ebola patients in Sierra Leone and that the situation in Liberia is now “dire.”

“Over the last weeks, there has been a significant surge in the epidemic – the number of cases has increased dramatically in Sierra Leone and Liberia, and the disease has spread to many more villages and towns,” the organization said in a statement. “After a lull in new cases in Guinea, there has been a resurgence in infections and deaths in the past week.”

At least 729 people have died since cases first emerged in March: 339 in Guinea, 233 in Sierra Leone, 156 in Liberia and one in Nigeria.

Two American health workers in Liberia have been infected, and an American man of Liberian descent died in Nigeria from the disease, health authorities there say.

Plans were underway to bring the two American aid workers â€” Nancy Writebol and Dr. Kent Brantly â€” back to the U.S. A small private jet based in Atlanta has been dispatched to Liberia. Officials said the jet was outfitted with a special, portable tent designed for transporting patients with highly infectious diseases.

While health officials say the virus is transmitted only through direct contact with bodily fluids, many sick patients have refused to go to isolation centers and have infected family members and other caregivers.

The fatality rate has been about 60 percent, and the scenes of patients bleeding from the eyes, mouth and ears has led many relatives to keep their sick family members at home instead. Sierra Leone is now sending teams door-to-door in search of Ebola patients and others who have been exposed to the disease.

Chan emphasized Friday that the general public “is not at high risk of infection,” but also said the Ebola virus should not be allowed to circulate widely.

“Constant mutation and adaptation are the survival mechanisms of viruses and other microbes,” she said. “We must not give this